In a magnetic recording device such as a HDD (Hard Disk Drive), a TMR (Tunneling Magneto Resistance) element is used as a reproducing element. The TMR element includes a magnetization pinned layer having a pinned magnetization direction, a magnetization free layer having a variable magnetization direction, and an intermediate layer interposed between the magnetization pinned layer and the magnetization free layer. In this structure, a tunneling-conduction oxide is used as the intermediate layer.
To increase recording density, the track width needs to be reduced, and, along with this request, there is a demand for a reproducing element having a smaller size in the track width direction.
Meanwhile, to reduce the size of a reproducing element and achieve a high transfer rate and a high S/N ratio, a reproduction resistance of 0.5 kΩ to 1 kΩ should be maintained. As a result, the areal resistance RA of the intermediate layer needs to be lowered. If the areal resistance RA is too low, a noise problem occurs due to spin torque, and it becomes difficult to increase current, resulting in difficulties in achieving high outputs. In view of this, a TMR element having an areal resistance RA between 0.1 Ωμm2 and 0.2 Ωμm2 is desirable. However, the decrease in the areal resistance of a TMR element is reaching its limit (approximately 0.3 Ωμm2), and there is a demand for a novel structure or material for the intermediate layer.
In response to such a demand, a current-constricting structure has been developed. The current-constricting structure has a metal conducting path in part of the insulating oxide layer serving as the intermediate layer. However, where a reproducing element using this current-constricting structure is made smaller in size, the number of conducting paths becomes smaller, resulting in wider variation in areal resistance.
In view of this, an intermediate layer containing a novel low-resistance oxide that differs from a tunneling-conduction oxide has recently been suggested through a different approach from the current-constricting structure. A first known example of such a low-resistance oxide layer is Cu/Zn—O/Zn, a second known example is Cu/Ga—O/ZnO, and a third known example is Cu/InZnO/Zn, in any of these examples, Cu, Ag, or the like is used immediately below the oxide layer. Therefore, the MR change rate or ΔR/R is 15% to 30%, and the areal resistance RA is 0.1 Ωμm2 to 0.3 Ωμm2.
To improve the resolution in the linear recording density direction, on the other hand, the gap between the two reproducing shields sandwiching the TMR element should be narrowed, and the thickness of the TMR element disposed in the gap needs to be reduced. However, the structure of a today's reproducing element includes many layers, such as an antiferromagnetic layer, a pinned layer, a nonmagnetic layer, and a free layer. Because of this, it is difficult to narrow the gap in the reproducing element.
As a means to solve this problem, a reproducing head including a reproducing element that utilizes a spin accumulation effect has been suggested. In this reproducing element, the antiferromagnetic layer and the pinned layer(s) can be disposed outside the gap. To achieve a high output and a high S/N ratio with this reproducing element, an interfacial oxide layer having an areal resistance RA of approximately 0.1 μm2 is preferably inserted into the structure.